This disclosure relates generally to journal air bearings, which are also known as hydrodynamic fluid film journal bearings or foil bearings.
As known, journal air bearings support rotatable components, such as a shaft within an air cycle machine of an aircraft. A typical journal air bearing arrangement includes a top foil, an intermediate foil, and a bump foil. The foils are received within a journal sleeves and wrapped around a rotatable component. The top foil is closer to the rotatable component than the other foils. Journal air bearings use a fluid, such as air, to support the component during rotation. There is little or no contact between the top foil and the rotatable component when the component rotates.
Some journal air bearings include a formed key that extends radially relative to the axis of rotation of the component. The formed key is received within a slot in the journal sleeve. The formed key contacts the edges of the slot to limit rotation of the foils relative to the component. The fluid that supports the component during rotation communicates through the clearance provided at the formed key. The fluid supporting the component is pressurized during rotation. The pressure of the fluid varies depending on the circumferential location relative to the slot. The varied pressures can destabilize the component. In the prior art, pressure of the fluid typically peaks about 180° from the formed key.